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NUCLEAR AND ISOTOPIC TECHNIQUES
MARINE POLLUTION MONITORING
FOR
A. Introduction
The greatest natural resource on the Planet, the World Ocean is both the origin of most life
forms and the source of survival for hundreds of millions of people. Pollution of the oceans
was an essential problem of the 20th century that was associated with the rapid
industrialization and unplanned occupation of coastal zones It continues to be a concern in the
21st century. The most serious environmental problems encountered in coastal zones are
presented by runoff of agricultural nutrients, heavy metals, and persistent organic pollutants,
such as pesticides and plastics. Oil spills from ships and tankers continually present a serious
threat to birds, marine life and beaches. Also, many pesticides that are banned in most
industrialized countries remain in use today, their trans-boundary pathway of dispersion
affecting marine ecosystems the world over. In addition to these problems, ocean dumping of
radioactive waste has occurred in the past, and might occur again, with authorised discharges
of radioactive substances from nuclear facilities into rivers and coastal areas contributing to
the contamination of the marine environment.
A trans-boundary issue, marine pollution is often caused by inland economic activities, which
lead to ecological changes in the marine environment. Examples include the use of chemicals
in agriculture, atmospheric emissions from factories and automobiles, sewage discharges into
lakes and rivers, and many other phenomena taking place hundreds or thousands of
kilometres away from the seashore. Sooner or later, these activities affect the ecology of
estuaries, bays, coastal waters, and sometimes entire seas, consequently having an impact on
the economy related to maritime activities.
In order to ensure the sustainable use of marine ecosystems it is necessary to measure critical
contaminants individually and to obtain reliable data on their source, dynamics and fate.
Nuclear and isotopic techniques provide a unique source of information for identifying
nuclear and non-nuclear contaminants and tracing their pathways in the environment, as well
as for investigating their biological effects. This review provides a short summary of the
application of nuclear techniques and isotopes as tools to track the source of contamination.
Emphasis is placed, in particular, on the use of nuclear techniques for the determination and
the tracking of organic pollutants.
B. Tracking Contaminants in the Marine Environment
through the Application of Isotopic Tracers
Determining pollution sources is one of the biggest issues in evaluating the incidence and
severity of contaminants in the marine environment. For the past 50 years, the impact of
human activity has aggravated environmental conditions in marine ecosystems. In effect, a
wide range of waste and discharge emerging from industries and activities undertaken at the
local, sub-regional and regional levels combine in the world’s ocean currents, resulting in a
global distribution of contaminants. To curb these phenomena it is imperative for countries to
apply environmental regulation that considers socioeconomic development on par with
environmental protection at local and global scales. However, effective environmental
regulation can only be accomplished if contaminant distributions are clearly linked to known
processes or sources. Stable carbon isotope analysis can help track sources of organic
pollutants. The stable isotopic composition of a contaminant in the environment is the end
result of a composite sequence of events. Chemicals produced from distinct sources by
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essentially different processes are expected to exhibit specific isotopic compositions that can
be used to identify sources.
One of the most significant advances in analytical chemistry in the past few years has been
the development of individual compound-specific stable isotope analysis (CSIA). This
technique, which is based on gas chromatography/isotope ratio mass spectrometry
(GC/IRMS) allows for the measurement of the carbon isotopic composition of individual
compounds within a complex mixture. CSIA of carbon is being used to uniquely identify
naturally occurring pollutants, such as polycyclic aromatic hydrocarbons (PAHs), chlorinated
solvents, polychlorinated biphenyls (PCBs) and crude oils and refined hydrocarbon products.
GC/IRMS can be used to measure the nitrogen and hydrogen isotopic composition of
individual compounds. The ability to monitor more than one isotopic composition greatly
improves the ability to identify the sources and processes controlling contaminant behaviour
in the environment. While GC/IRMS systems are not yet available to measure the chlorine
isotopic composition of individual chlorinated contaminants, chlorine isotope analysis is a
useful technique for studying the sources and fate of common chlorinated contaminants.
Molecular level radiocarbon (carbon-14) analysis of compounds is also used to determine
compounds that are either natural products or derived from industrial synthesis.
B.1. Hydrocarbons and oils
Hydrocarbons and oil products are a group of pollutants that have complex and diverse
composition and which cause various impacts on living organisms - from physical and
physicochemical damage to carcinogenic effects. The estimated average annual amount of oil
entering the marine environment from ships and other sea-based activities, based on data from
1988-1997 is 1,245,200 tonnes/year [III-18.]. Until recently, source apportionment studies of
hydrocarbons in the environment mostly relied on molecular fingerprint recognition.
Nevertheless, processes affecting hydrocarbons in the marine environment (evaporation,
dissolution, photooxidation, biodegradation, etc.) might alter the initial hydrocarbon
molecular profiles due to the preferential compound losses or degradation, increasing the
chances of ambiguity in using molecular profiles in source identification.
Petroleum genesis induces a wide range of isotopic signals, which in general differ
significantly from the isotopic compositions of unpolluted marine ecosystems. The complex
isotopic fractionation patterns induced by physical and biological processes result in
characteristic carbon-13/ carbon-12 ratios that can be used to classify crude oils, petroleum
products and tars. While most emphasis has been placed on the use of bulk carbon isotopes
for source and correlation purposes, a number of forensic applications include other stable
isotopes. Sulphur, nitrogen and deuterium isotopic abundances also reflect source and
geological histories of formation, which contain oil-field specific ratios. The characteristic
isotopic ratios of these elements can be exploited to "fingerprint" oils spilled into the
environment in order to determine the source or sources. While bulk measurements provide
useful information, the compound specific isotope analysis of individual components within a
specific type of oil represents a unique signature of its origin and maturation.
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FIG. III-1. The red line shows the route taken by the oil carrier Prestige, from the time it
started leaking oil on 13/11/2002 until it sank in 19/11/2002. The dark smudges indicate the
oil spill detected by satellite remote sensing. Data compiled with nuclear techniques
complemented with satellite imagery can be instrumental in identifying pollution sources.
In conjunction with the existing tools of biomarkers, GC–IRMS has been used for forensic
identification of gasoline and crude oil spills. For example, it allows correlating hydrocarbons
spilled in aquatic environments with their suspected source(s) based on comparison of the
isotopic composition of individual hydrocarbons. Differences in the isotope composition of
individual compounds within a gasoline or crude oil sample are immediately apparent and
reflect their different origins. In this regard, although weathering can result in a remarkable
loss of volatile hydrocarbons, δ13C values of non-volatile and semi-volatile compounds are
unaffected by weathering and their isotopic profiles can be used to identify and trace the
source of an oil spill.
After the Erika spill 1 , bulk and individual compound isotopic analyses on oil residues
sampled along the Atlantic Coast of France allowed the unambiguous differentiation of
samples related to the Erika oil spill from those due to other tar ball incidents [III-3]. CSIA of
carbon was also recently used by the IAEA’s Monaco Laboratory in conjunction with nonnuclear fingerprinting techniques to investigate the sources of the oil slicks sampled in the
vicinities of the wreck more than four years after the Prestige 2 accident (Fig. III-1). The
isotopic data was used to ascertain that the oil from the slicks matched the oil originally
carried by the Prestige tank (Fig. III-2).
The Maltese tanker “Erika” broke in two parts close to the Atlantic coast of France on December 12,
1999. It is believed about 10,000 tons of oil spilled into the sea.
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On November 13, 2002, the tanker “Prestige” vessel broke in two at 240 Km off NW Spain and sunk
at more than 3000m depth with about 58,000 tonnes of heavy fuel oil and leaking from several cracks
in the structure.
1
3
-27.00
Erika oil
Prestige oil
δ13C (‰)
-28.00
sinking area
-29.00
-30.00
-31.00
-32.00
-33.00
C16
C17+Pr C18+Ph C19
C21
C22
C23
C24
FIG. III-2. Comparison of the carbon isotopic signatures of the fuel oil found above the
Prestige wreck in October 2006 with the one originally carried by the tanker in 2002 and that
from the Erika ([III-3]). In axis x the variation in C-13 is reported for the different
hydrocarbons examined as reported on the axis y. (PhD Thesis: Elourdui-Zapatarietxe del
Aguila, 2009)
Photo Credit: Elourdui-Zapatarietxe del Aguila, 2009
The measurement of hydrogen isotope ratios in specific petroleum hydrocarbons is also a
powerful technique to identify the source of the contaminant since the hydrogen isotope ratios
of crude oil hydrocarbons show a wide compositional variation and are conserved during
aerobic biodegradation. In the future, both hydrogen and carbon isotopic data should be
considered when tracing contamination sources and monitoring biodegradation.
In addition to the stable isotopes, radiocarbon (carbon-14) measurements can potentially
provide information on oil contamination. Petroleum-derived organic matter is carbon-14
free, on the other hand total marine organic matter is labelled with carbon-14 originating from
both C-14 produced naturally in the atmosphere by cosmic radiation and in nuclear weapons
explosions. Therefore, the absence of the carbon-14 signal in contaminants derived from
fossil-fuel (as the complete decay during the oil's geological formation) provides a useful
quantitative indication of the contribution of petroleum carbon to the total marine organic
matter.
B.1.1. Polycyclic aromatic hydrocarbons (PAHs)
Polycyclic aromatic hydrocarbons (PAHs) are a widespread class of organic contaminants
that enter the marine environment mostly due to atmospheric deposition and oil spills. They
can be formed during incomplete combustion processes (pyrolitic origin) of organic matter
(e.g. coal, oil, wood), and are also major constituents of crude oil (petrogenic origin). They
might also derive from the biological and physiochemical alteration of organic matter, which
occurs in sediments after deposition (diagenetic origin). As some PAHs exhibit mutagenic
and carcinogenic properties, the knowledge of their sources is of key importance due to their
eco-toxicological nature, which present long-term health effects on nearshore marine systems,
affecting ecological processes, public health and social and commercial use of marine
resources. In this context, molecular stable carbon isotopic composition of PAHs by
GC/IRMS is a powerful tool for use in conjunction with molecular fingerprint examination
for studying the sources and environmental fate of hydrocarbons in the modern environment.
For instance, atmospheric contaminants from combustion source materials such as soot from
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biomass, natural gas, coal burning and vehicle exhausts might be tracked to source materials
because of the isotope signals of the PAH products [III-5, III-1].
Other studies on carbon isotopic analysis of PAHs in sediment samples near a former gasmanufacturing plant in Illinois indicated that the hydrocarbons were not the same as the tarry
soil samples recovered from the gas plant ([III-19]. The dominant signatures identified in the
surface sediments came from a mixture of PAH sources such as coal tars and carburetted
water gas tars. Source apportionment might be complex because the range of δ13C values of
PAHs originating from different combustion processes such as diesel, coal, gasoline, and
wood burning smoke might overlap each another. However, it has been shown that distinct
isotopic signatures are produced by primary petroleum and combustion-related PAH sources,
as well as between the combustion of C43 plants using the C4 photosynthetic pathway, termite
nests or biogenic natural gas. On the other hand, radiocarbon dating of individual PAHs using
off-line gas chromatography/accelerator mass spectrometry (GC/AMS) is emerging as a
promising tool to apportion fossil and contemporary or biogenic sources of compounds in
marine samples [III-6, III-8].
B.2. Halogenated organic compounds
Most of the halogenated organic compounds belong to the category of persistent organic
pollutants, which have a tendency to bioaccumulate along the food chain, causing toxic and
mutagenic effects. A few studies have reported the carbon-13 compound specific isotope
analysis (CSIA) of commercial polychlorinated biphenyl (PCB) and polychlorinated
naphthalene mixtures (PCN) such as Aroclors, Kanechlors, Phenoclors, etc. to establish
baseline data for future identification of these anthropogenic contaminants. Recent studies
have also detected some bipyrrolic halogenated organic compounds worldwide and
accumulating in the marine food webs [III-7]. To date, it has been difficult to determine
whether these compounds are natural products or derived from industrial synthesis.
Radiocarbon (carbon-14) is a tracer used to distinguish between natural or synthetic
compounds. In this context, radiocarbon analysis may be used as a tool to establish the origin
of halogenated organic compounds since all recent natural products have modern or
contemporary carbon-14 levels. In contrast, synthetic goods derived from petrochemical
products contain no measurable carbon-14.
B.3. Perchlorate
The widespread introduction of synthetic and agricultural perchlorate (ClO4−) into the
environment has contaminated numerous municipal water supplies – in the marine
environment, contamination by this compound presents an unequivocal problem. Various
potential sources of ClO4− are present, including agriculture (past or present), fireworks
manufacture and use, military bases including missile storage and launch facilities, road-flare
runoff, and lawn fertilizer, among others. Stable isotope ratio measurements of chlorine and
oxygen have been applied for discrimination of different ClO4− sources in the environment.
More recently, the characteristic chlorine-36 and chlorine-37 isotopic abundances found in
the three principal sources of ClO4− present in the environment allowed these sources to be
distinguished from each other. These results may have immediate forensic applications in
delineating the sources of ClO4− in water supplies and foodstuffs, and they may provide
important constraints for determining the natural production mechanism of ClO4− [III-9].
C4 designates the photosynthetic pathway of the plants that fix carbon to produce a four-carbon
molecules, in contrast to the majority of plants that produce C3 molecules
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5
C.
Stable Isotopes to Study Bioremediation
In situ bioremediation has emerged as one of the most important alternatives to mitigate the
damage caused by marine oil spills and other hydrocarbons. However, it is imperative that
biotransformation processes are accurately understood and quantified. Quantification of
intrinsic biodegradation may also reduce site remediation costs where engineered remediation
is instituted. For that, the natural abundance of stable isotopes of essential elements involved
in the biodegradation processes (carbon, hydrogen and oxygen) are used to monitor the
occurrence of in situ biodegradation, the pathways of degradation and the rates and extent of
biodegradation of fuel or chlorinated hydrocarbons. Monitoring of in situ biotransformation
using stable isotopes may be achieved by the analysis of isotopic compositions (i) of the
products of degradation, (ii) the residual fractions of the contaminant, and (iii) dissolved
inorganic carbon of the water, because isotopic fractionation results in preferable degradation
of chemical bonds with lighter compared to heavier isotopes 4 [III-10]. Carbon dioxide
produced by organic matter oxidation, inorganic carbon dissolution, or contaminant
hydrocarbon degradation has characteristic carbon-13 isotope ratios. Their carbon-13 values
are useful tools for the assessment of in situ biodegradation in complex environments.
Furthermore, the oxygen isotopic compositions of molecular oxygen, nitrate, and sulphate in
complex systems are affected primarily by microbial processes, and isotopic fractionation
during microbial respiration produces a significant change in the δ18O of the residual
molecules. The combination of the isotopic compositions of CO2 and O2 help to distinguish
between aerobic and anaerobic production of CO2 and for quantifying microbial respiration
rates [III-11].
In general, quantitatively differentiating the effects of bio-transformations from physical
processes on contaminants is challenging. However, CSIA allows for the rapid determination
of carbon and hydrogen isotopic signatures of organic compounds over the course of
biodegradation by measuring the two stable isotopes of carbon and of hydrogen. CSIA is used
as an indicator parameter to assess the in situ biodegradation of the chlorinated solvents and
fuel oxygenates, e. g. methyl tert-butyl ether. In comparison with the carbon isotopes, the
hydrocarbon isotopes display large variation in the deuterium isotope values. Indeed, the
hydrogen isotope ratio of the light petroleum hydrocarbons can also be used to monitor in situ
bioremediation of crude oil contamination.
D. Stable isotopes to track bio-magnification of
contaminants
Many persistent organic pollutants (POPs) present in the aquatic environment tend to
accumulate in aquatic organisms due to their hydrophobicity. The widespread and persistent
nature of these chemicals has been linked to various environmental effects, including
pollution of water, sediments, and of the aquatic food chain. The health effects posed by
exposure to these chemicals include disturbances ranging from disorders of the nervous or
immune system, to increases in the risk of certain cancers. In the last two decades, the study
of biomagnification5 profiles of POPs including PCBs, PAHs, organotins and trace elements
through aquatic food webs has been facilitated through stable isotope ratio analysis of
bioelements, such as carbon and nitrogen. In general, the stable nitrogen isotope ratio δ15N
increases by 3-4‰ per trophic level in a food chain. Thus, the value of δ15N is suitable for
determining the trophic position of each organism in a food web. The stable carbon isotope
The stability of a chemical bond depends on the isotopic composition. Bonds between lighter isotopes
(e.g. 12C-2H) are more readily broken than bonds between heavier isotopes (e.g. 13C-2H).
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Biomagnification is the increase in concentration of a substance that occurs in a food chain as a
consequence of persistence, food chain energetic and low rate of internal degradation of the substance.
4
6
ratio, δ13C, is enriched slightly by about 1‰ per trophic level, enabling its use in identifying
primary carbon sources in a food web [III-12].
E. The Use of Isotope Labelling to Study the Fate of
Contaminants
Understanding contaminant input routes, transport mechanisms and environmental conditions
provides the basis for determining the fate of contaminants. This enables us to explain and
anticipate contaminant impacts on environmental biodiversity and human health. Data on the
environmental fate of contaminants are required in order to determine the potential of a
pollutant to reach coastal waters, including information on its hydrolysis, photolysis and
aquatic metabolism. The introduction of a labelled tracer into a controlled experimental
system permits the investigation of the interaction of individual contaminants with biotic and
abiotic components of the environment. Classically, carbon-14 labelled xenobiotics 6 are
applied to study the fate of organic compounds in laboratory mesocosms7. The radioactivity
of the label is used to trace the mineralization (14CO2), the portion of extractable material and
to quantify the part of the label incorporated within the sediment-bound residues or
accumulated into the organisms. Compared with the carbon-14 technique, the carbon-13
labelling method allows for direct structural assignments of the compounds by mass
spectrometry, easy handling and can be performed in the field.
F.
Stable isotopes to study eutrophication
The rise in the human population in coastal watersheds and changes in land use has led to
increases in the delivery of nutrients in aquatic environments. The resulting eutrophication of
coastal waters has many adverse effects in the marine environment, through disturbance of
ecological balances and fisheries, and through interference with recreational activities and
quality of life. Eutrophication – nutrient enrichment leading to elevated production of
particulate organic matter – is one of the profound impacts caused on coastal ecosystems by
human activity. Increased nutrients loading can lead to blooms of toxic red tides including
enhanced primary production, changes in community structure, increases in sedimentation
and oxygen consumption, oxygen depletion in the bottom water and sometimes the death of
benthic animals and fish. These adverse effects have prompted the search for suitable
indicators of eutrophication to assess water quality of aquatic ecosystems [III-13]. Stable
nitrogen isotope ratios (15N/14N; i.e. δ15N) have been widely used as indicators of
anthropogenic eutrophication in aquatic ecosystems. Sewage water typically has a high
nitrogen stable isotope ratio (δ15N) due to denitrification during the treatments. Applications
of nitrogenous fertilizer to agricultural farmlands lead also to an enhancement of soil denitrification and increase the δ15N in groundwater. In contrast, the δ15N of nitrogen derived
from atmospheric deposition and nitration fixation by bacteria are much lower. Groundwater
and sedimentary organic matter with an elevated δ15N appears to act as an indicator of the
level of anthropogenic nitrogen loads to coastal waters, and the δ15N delivered to the coastal
waters are transferred to the food chain. Nitrogen isotope ratios of marine producers may be
used to identify incipient eutrophication in coastal waters.
The dual isotope analysis of nitrate (NO3-) in water (δ15N and δ18O) is used to further
differentiate sources of nitrate when δ15N ranges overlap. For example, δ18O can be used to
separate NO3 fertilizer from soil nitrogen and ammonia (NH4) in fertilizer and rain.
Chemical found in an organism, but not normally produced or expected to be present in it.
A mesocosm refers to “an experimental system that simulates real-life conditions as closely as
possible, whilst allowing the manipulation of environmental factors”.
6
7
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Additionally, both the δ18O and δ15N of the residual nitrate increase systematically as a result
of denitrification. Other isotopes, e. g. sulphate oxygen and sulphur isotopes in river water
might also enable the discrimination between natural (geological, sea water, geothermal and
volcanic) and anthropogenic sources such as fertilizers. Employment of more than one
isotopic proxy will allow for a more accurate identification of the nutrient sources available to
primary producers.
The analysis of proxy records preserved in sediments often provide the only way to
reconstruct environmental change in areas impacted by eutrophication and to establish preimpact baselines. Stable carbon isotope ratios in microfossils provide a tool for reconstructing
historical environments, in particular organic carbon delivery to sediments. Increased organic
matter inputs typically lead to a decrease in carbon-13 in the carbonate shells with a
concomitant Carbon-13 (13C) increase in the organic matter. Furthermore, the main indicators
of enhanced primary production linked to eutrophication is phytoplankton. Their remains, and
the specific chemical markers derived from them (e.g. lipid biomakers) [III-14], can be used
to track changes in plankton communities in response to eutrophication. Moreover, since
eutrophication leads to raised 13C values due to increased marine phytoplankton production,
the compound specific carbon isotope analysis of lipid biomarkers reflect the strength of the
eutrophication.
G. Use of Radioisotopes for the Detection of Toxins
in Harmful Algae Blooms (HABs)
One of the most worrisome manifestations of HABs is that certain algal species produce
toxins that can accumulate in seafood products (predominantly shellfish and fish) and then
pose a risk to human consumers. Fig.III-3 shows a map of the regions affected by the
phenomena of HABs and the increase of HABs events worldwide.
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FIG. III-3. Harmful Algal Blooms (HABs) - a growing concern worldwide – produce toxins
that accumulate in marine species rendering them unfit for human consumption (Data from
IOC-UNESCO).
The heterogeneity within and among toxin classes makes toxin detection and quantification
challenging. Different species of algae - examples are shown in Fig III-4 - produce different
types of toxins. Numerous approaches to toxin detection have been developed, generally
categorised as whole animal (in vivo) bioassay, in vitro bioassays, and quantitative
instrumental analysis. One useful technique of analysis employs radioisotopes – the receptor
binding assay (RBA). The RBA is a technique based on the function, or pharmaceutical
activity of the toxins – i.e., the highly specific interaction of a toxin with a biological receptor.
For example, the saxitoxins (STXs) are toxic because they bind to and block sodium channels
in certain types of human tissues, disrupting muscle function and leading to paralysis and
death. The sodium channel is the logical receptor to be used in a receptor binding assay for
STXs. RBAs have been developed for toxins that affect the sodium channel (PSP, NSP and
CFP toxins) [III-15, III-17] and glutamate receptor (ASP toxins) [III-15, III-16]. The binding
of toxin molecules containing a radionuclide such as Tritium (3H) to the receptor sites is then
determined by a liquid scintillator counter.
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FIG. III-4. Example of harmful microalgae.
H. Long-lived Radionuclides and Isotope Ratios
Measurements
With the advent of advanced mass spectrometric (MS) techniques, long-lived radionuclides
determination is no longer performed by counting decays, but by employing MS techniques
because of their outstanding capacity to determine precise and accurate isotopic abundances
and isotopic ratios. Isotope ratio measurements have been applied increasingly for
investigating the fine isotope variations in nature, age dating of geological samples,
provenance determination of environmental contamination, nuclear material accounting and
pollution control, and for biological studies with tracer experiments. Applied to marine
ecosystems, the technique assists in determining and tracking sources of contamination.
Moreover, mechanisms of transport of contaminants as well as their accumulation/desorption
from sediments can be followed.
Recent developments in mass spectrometry with the developments of better performing
magnetic sectors and their coupling to electrostatic sectors have brought a new dimension to
this field. In addition to its simple and robust sample introduction, high sample throughput,
and high mass resolution, the flat-topped peaks generated by this technique provide for
accurate and precise determination of isotope ratios. These features, in combination with the
ability of the inductively coupled plasma source to ionize nearly all elements in the periodic
table, have resulted in an increased use of Inductively Coupled Plasma – Mass Spectrometry
(ICP-MS) for such measurements in various sample matrices. Moreover the technique can be
coupled with chemical separation on-line methods such as liquid chromatography, allowing a
fast throughput of samples avoiding manual radiochemical separations. Fig. III-5 shows the
simultaneous separation and determination of actinides and lanthanides in marine sediment by
ICP-MS on-line coupled to a chromatographic system
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FIG. III-5. Simultaneous chromatographic separation and on-line mass spectrometric
determination of lanthanides and actinides in a marine sediment sample. This is instrumental
in determining isotope ratios that are important in identifying and tracking sources of
contamination. (M. Betti, ITU Summer School 2003 on “Actinide Science and Applications”;
EU Joint Research Centre - ITU, Karlsruhe)
The ability to measure isotope ratios allows also the use of isotope dilution as a calibration
strategy in ICP-MS, along with the more common approaches of external calibration and the
standard additions. An isotope ratio is far more robust than a signal intensity, which makes
isotope dilution mass spectrometry (IDMS) a very reliable approach. When carried out with
the utmost care and control of all factors affecting the final uncertainty, IDMS provides
highly accurate and precise results and therefore is the best calibration strategy for
certification measurements in the production cycle of various certified reference materials.
I.
Radiometric Dating / Radio-Chronology
Historical records of organic and inorganic pollution combined with isotopic fingerprinting of
contaminant sources are a powerful argumentative tool to link the evolution of contaminants
with socioeconomic decisions. An investigation conducted by scientists from Cuba and IAEA
specialists, examined whether pollution in the marine sediment environment was responsible
for a ten-year decrease in lobster catch in Batabano Bay (Cuba). The first conclusion derived
from the dating and pollution measurements of this study is that in general pollution levels in
the Batabano Bay are very low and have not significantly changed during the period of
interest, except for some local hotspots. The study demonstrates that in order to reconstruct
changes in pollution over time environmental archives (i.e. marine sediments, corals) are
helpful as they store information on the pollution during the geological past. A record of
pollution is obtained by combining age-dating with the measurements of the pollutant of
interest.
Most age-dating techniques are based on the radioactive decay rates of the different
radionuclides present in the system. In table III-1 the most common dating techniques are
presented.
Three kinds of radionuclides are normally used for age-dating of marine archives:
anthropogenic, cosmogenic and natural radionuclides. The first significant appearance of
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anthropogenic radionuclides - e.g. Cesium -137 (137Cs) and plutonium - in the environment
was a result of atmospheric nuclear bomb tests, which peaked in 1963. Thus, the first
appearance of 137Cs in sediments can be used as a time marker. Cosmic radiation interacts
with our atmosphere and forms so called cosmogenic radionuclides such as Carbon-14 (14C)
and Beryllium-10 (10Be) by particle reaction. Carbon combines with O2 and is incorporated
into living organisms. When the organism dies, the 14C concentration in the dead organism
will be a function of time and can consequently be used in radio-chronology. For minerals 14C
cannot be used as it is not incorporated in the matrix. For such material the Uranium-, and
Thorium-decay series and primordial radionuclides (e.g. Potassium/Argon (40K/40Ar) decay
system) are applied for age determination. The dating technique based on lead-210 (210Pb) is
frequently applied for dating of recent (< 100 years) sediments. Table III-1 summarises the
most common applications.
In addition, one technique called luminescence dating can be used for mineral material. Not
based on the measurements on the decay rate, rather, this technique uses the ionizing
absorbed dose for measurement.
J.
Conclusion
The unique diagnostic power of isotope studies can help to understand the threats to the
marine environment. Most major pollution problems facing the marine environment can only
be investigated using nuclear and isotopic techniques, which offer the diagnostic and dynamic
information needed to identify the source of contamination, its history of accumulation, its
environmental pathways and its impact on the environment. Such information is needed to
make cost effective mitigation decisions.
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Table III-1: The most common applications for radiometric dating/ radio-chronology
Dating
Application
Principles:
Technique
and Range
Anthropogenic Sediments, Time of
radionuclide
past ~ 50
release of
137
( Cs,
years
anthropogenic
plutonium)
radionuclides
from e.g.
nuclear
facilities sets a
time marker in
environmental
archives
210
Pb
Sediments, The decrease
< 100 years of 210Pb in
sediments is a
function of
time.
14
C
Organic
Decay of 14C
material,
in organisms.
<50 000.
Luminescence
dating
Uranium
series
(230Th/234U,
234 238
U/ U)
dating
Dating of
minerals in
e.g.
sediments,
< 400 000
years
Minerals
(feldspar,
quartz) “store”
information on
the absorbed
dose they have
received over
time. This
“memory” can
be recorded
and can be
translated in
age
information
Sediments, Disequilibriu
corals, < 1.5 m between
mill years
daughter and
parent leading
to either a
deficiency or
an excess of
the daughter
nuclides which
can be
measured as a
function of
time.
Further reading:
Environmental records of anthropogenic impacts on
coastal ecosystems: An introduction, J.-A. SanchezCabeza, and E.R.M. Druffel, Marine Pollution
Bulletin
Volume 59, Issues 4-7, 2009, Pages 87-90
Ivanovich, M., & R. S. Harmon, 1992. Uranium
series disequilibrium: Application to environmental
Problems. Clarendon Press, Oxford, 571 p.
http://www.radiocarbon.org/
Faure, G., 1986. Principles of Isotope Geology.
John Wiley & Sons, 589 p.
http://www.c14dating.com/
http://www.nclr.risoe.dk/
http://crustal.usgs.gov/laboratories/
luminescence_dating/technique.html
http://www.onafarawayday.com/Radiogenic/index.h
tm
Ivanovich, M., & R. S. Harmon, 1992. Uranium
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